The present invention relates to a thermal printer head for a facsimile printer, in particular, relates to such a thermal head having a linear continuous heater line, which is manufactured through a thick film resistor technique.
Conventionally, a thermal head has a plurality of thermal cells each of which is individually heated in order to heat a treated thermal paper selectively. That thermal paper changes color upon heated, and the thermal printing is accomplished by those thermal cells.
However, that prior thermal head with separated thermal cells has the disadvantage that the structure is complicated and/or the manufacturing cost of the same is high, since many cells insulated from each other must be mounted in a short length, and the density of the cells is extremely high.
Another conventional thermal head is shown in FIG. 1, in which a thermal head has a linear continuous line manufactured through a thick film resistor technique. As a thermal head is merely a continuous line, but has no separated thermal cells, the manufacturing process of that linear thermal line is simple. In FIG. 1, the reference numeral 1 is a thermal resistor line, 2 is a diode, and 3 is a transistor switch.
The thermal resistor line 1 has a plurality of lead wires for all the cell portions (r.sub.1, r.sub.2, r.sub.3, et al.) on both the sides of the line, alternately. Those cell portions (r.sub.1, r.sub.2, r.sub.3, et al.) operate substantially as a thermal cell. The lead wires are provided on the substrate on which the thermal line 1 is provided. The first group of lead wires on one side of the thermal line 1 are coupled with the transistor switches 3, each base input of which is provided with an input signal (B.sub.1, B.sub.2, B.sub.3, et al.). The second group of lead wires on the other side of the thermal line 1 are classified further to two groups, alternately, and the first sub-group of lead wires are coupled with the first power source S.sub.1 through respective diodes 2, and the second sub-group of lead wires are coupled with the second power source S.sub.2 through the respective diodes 2.
When the first power source S.sub.1 is ON, the cells (r.sub.2, r.sub.3), (r.sub.6, r.sub.7), (r.sub.10, r.sub.11), (r.sub.14, r.sub.15), are energized according to the input signals at the inputs (B.sub.1, B.sub.2, et al.). Next, when the second power source S.sub.2 is ON, the cells (r.sub.0, r.sub.1), (r.sub.4, r.sub.5), (r.sub.8, r.sub.9), (r.sub.12, r.sub.13), are energized according to the input signal at the inputs (B.sub.1, B.sub.2, et al.). For instance, when the first power source S.sub.1 is ON, and the input terminals B.sub.2 and B.sub.5 have the input signals, then, the cells r.sub.3 and r.sub.10 are heated. It should be noted in this case that another current path is provided from the first power source S.sub.1 through the diode 2, the cells r.sub.7, r.sub.8, r.sub.9, to the input B.sub.5, however, the intermediate cells r.sub.7 through r.sub.9 are not heated enough to print on a thermal paper. Because the current in said another current path is small because of the series connection of a plurality of resistor cells, and thus, the temperature in those intermediate cells is not much increased.
However, the thermal head of FIG. 1 has the disadvantage that many diodes and transistors are necessary for energizing selectively each cell. In the configuration of FIG. 1, if the number of transistors and/or diodes were reduced, undesired cells would be heated to print a thermal paper, and no clear printed copy would be obtained in a facsimile reception system.